Methods of fuel cell operation with bi-directional inverters

ABSTRACT

A microgrid system includes first and second DC power sources electrically connected to respective first and second DC electrical power busses, a first uninterruptable power module electrically connected to the first DC electrical power bus and configured to be connected to an alternating current (AC) load, a second uninterruptable power module electrically connected to the second DC electrical power bus and configured to be connected to the AC load, a first bi-directional AC/DC inverter having a DC end and an AC end, where the first DC electrical power bus is connected to the DC end of the first bi-directional AC/DC inverter, a second bi-directional AC/DC inverter having DC and AC ends, where the second DC electrical power bus is connected to the DC end of the second bi-directional AC/DC inverter, and an AC electrical power bus electrically connected to the first and second bi-directional AC/DC inverters at their AC ends.

FIELD

The present invention is generally directed to power generation systemsand, in particular, to a fuel cell system that efficiently manages fuelcell power output to address degradation of fuel cell system powersupply using bi-directional inverters.

BACKGROUND

Electrochemical devices, such as fuel cells, can convert energy storedin fuels to electrical energy with high efficiencies. In a fuel cellsystem, such as a solid oxide fuel cell (SOFC) system, an oxidizing flowis passed through the cathode side of the fuel cell while a fuel inletflow is passed through the anode side of the fuel cell. The oxidizingflow is typically air, while the fuel flow can be a hydrocarbon fuel,such as methane, natural gas, pentane, ethanol, or methanol. The fuelcell enables the transport of negatively charged oxygen ions from thecathode flow stream to the anode flow stream, where the ion combineswith either free hydrogen or hydrogen in a hydrocarbon molecule to formwater vapor and/or with carbon monoxide to form carbon dioxide. Theexcess electrons from the negatively charged ion are routed back to thecathode side of the fuel cell through an electrical circuit completedbetween anode and cathode, resulting in an electrical current flowthrough the circuit.

SUMMARY

According to one embodiment, a microgrid system includes a first DCpower source electrically connected to a first DC electrical power bus,a second direct current (DC) power source electrically connected to asecond (DC) electrical power bus, a first uninterruptable power moduleelectrically connected to the first DC electrical power bus andconfigured to be connected to an alternating current (AC) load, a seconduninterruptable power module electrically connected to the second DCelectrical power bus and configured to be connected to the AC load, afirst bi-directional AC/DC inverter having a DC end and an AC end,wherein the first DC electrical power bus is connected to the DC end ofthe first bi-directional AC/DC inverter, a second bi-directional AC/DCinverter having a DC end and an AC end, wherein the second DC electricalpower bus is connected to the DC end of the second bi-directional AC/DCinverter, and an AC electrical power bus electrically connected to thefirst and the second bi-directional AC/DC inverters at their AC ends.

According to another embodiment, a microgrid system comprises a firstdirect current (DC) power source electrically connected to a first DCelectrical power bus, a second DC power source electrically connected toa second DC electrical power bus, a first uninterruptable power moduleelectrically connected to the first DC electrical power bus andconfigured to be connected to an alternating current (AC) load via atleast one load electrical power bus, a second uninterruptable powermodule electrically connected to the second DC electrical power bus andconfigured to be connected to the AC load via the at least one loadelectrical power bus, a first AC/DC inverter having a DC end and an ACend, wherein the first DC electrical power bus is connected to the DCend of the first AC/DC inverter, a second AC/DC inverter having a DC endand an AC end, wherein the second DC electrical power bus is connectedto the DC end of the second AC/DC inverter, an automatic transfer switch(ATS) having a load terminal, an emergency terminal, and a normalterminal configured to be connected to an electrical power utility grid,a first AC electrical power bus electrically connected to the first andthe second AC/DC inverters at their AC ends, and electrically connectedto the load terminal of the ATS, and a second AC electrical power buselectrically connected to the emergency terminal of the ATS and to theat least one load electrical power bus.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fuel cell system according to variousembodiments.

FIG. 2 is a schematic side cross-sectional view of a hot box accordingto various embodiments.

FIG. 3 is a block diagram of a fuel cell microgrid system havingbi-directional inverters according to some embodiments.

FIG. 4 is a block diagram of a fuel cell microgrid system havingbi-directional inverters and configured for selective electrical powerutility grid isolation according to some embodiments.

FIG. 5 is a block diagram of a fuel cell microgrid system havingbi-directional inverters and auxiliary electrical power storage and/orelectrical power dissipation according to some embodiments.

FIG. 6 is a process flow diagram for managing a fuel cell microgridsystem according to some embodiments.

FIG. 7 is a process flow diagram for managing a fuel cell microgridsystem according to some embodiments.

FIG. 8 is a process flow diagram for managing a fuel cell microgridsystem according to some embodiments.

FIG. 9 is a process flow diagram for managing a fuel cell microgridsystem according to some embodiments.

FIG. 10 is a block diagram of a fuel cell microgrid system havinginverters and an ATS configured for selective electrical power utilitygrid isolation according to some embodiments.

DETAILED DESCRIPTION

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.References made to particular examples and implementations are forillustrative purposes, and are not intended to limit the scope of theclaims.

Various embodiments include electrical circuits, electrical components,and methods for managing a microgrid system, such as a fuel cellmicrogrid system to address degradation of and imbalance in fuel cellmicrogrid system electrical power supply. In some embodiments, the fuelcell microgrid system may be configured to selectively electricallyconnect parallel power module clusters via bi-directional alternatingcurrent (AC)/direct current (DC) inverters. In some embodiments, inresponse electrical power undersupply on a first DC electrical powerbus, due to degradation and/or failure of a first power module and/or afirst power module cluster, a first bi-directional AC/DC inverter may beconfigured to selectively electrically connect the first DC electricalpower bus to an AC electrical power bus. The first bi-directional AC/DCinverter may be configured to import and rectify AC electrical powerfrom the AC electrical power bus to provide DC electrical power to thefirst DC electrical power bus. In some embodiments, the AC electricalpower imported by the first bi-directional AC/DC inverter may include ACelectrical power from an electrical power utility grid. In someembodiments, in response to electrical power oversupply on a second DCelectrical power bus, generated by a second power module cluster, asecond bi-directional AC/DC inverter may be configured to selectivelyelectrically connect the second DC electrical power bus to the ACelectrical power bus. The second bi-directional AC/DC inverter may beconfigured to export and invert DC electrical power from the second DCelectrical power bus to provide AC electrical power to the AC electricalpower bus. In some embodiments, the AC electrical power imported by thefirst bi-directional AC/DC inverter may include the AC electrical powerexported by the second bi-directional AC/DC inverter.

Fuel cell microgrid systems can be configured with multiple power moduleclusters electrically connected in parallel to a load and configured toprovide equal amounts of electrical power to the load to satisfy a loaddemand. When any of the power module clusters cannot supply the equalamount of electrical power, for example due to degradation and/orfailure of a power module of the power module cluster, the powersupplied the power module clusters becomes unequal. In response, due tothe imbalance in electrical power provided by each of the power moduleclusters, a fuel cell microgrid system can be configured to reduce theelectrical power supply to the load from the power module clusters sothat each power module cluster supplies a lower equal amount ofelectrical power to the load. The lower equal amounts of electricalpower can be based on an electrical power supply of the power modulecluster having a lowest electrical power generation capacity. As such,the combined electrical power supply to the load by the power moduleclusters is reduced. Power module clusters that can produce electricalpower greater than the lower equal amount of electrical power to theload are underutilized to power the load. Load drop can occur when theload demand is higher than the combined electrical power supply of thepower module clusters using the lower equal amount of electrical power.

The embodiments described herein may alleviate the foregoing issues ofmicrogrid systems, such as fuel cell microgrid systems configured withmultiple power module clusters electrically connected in parallel to aload and configured to provide equal amounts of electrical power to theload to satisfy a load demand. The microgrid system may include anynumber of power module clusters, such as fuel cell power module clustersand/or other power source power module clusters, electrically connectedin parallel to the load, such that the multiple power module clustersmay provide either equal or unequal amounts of electrical power to theload to satisfy a load demand, based on the microgrid status. The powermodule clusters may be electrically connected to and provide DCelectrical power to DC electrical power busses. The microgrid system mayinclude any number of bi-directional AC/DC inverters configured toselectively electrically connect the DC electrical power busses to an ACelectrical power bus. Each bi-directional AC/DC inverter may beconfigured to export and invert DC electrical power from a DC electricalpower bus to provide AC electrical power to the AC electrical power busin response to a voltage on the DC electrical power bus greater than athreshold voltage. Each bi-directional AC/DC inverter may be furtherconfigured to import and rectify AC electrical power from the ACelectrical power bus to provide DC electrical power to a DC electricalpower bus in response to a voltage on the DC electrical power bus lessthan a threshold voltage. In some embodiments, the threshold voltage maybe a voltage at which equal electrical power supply from each of thepower module clusters may satisfy the load demand. In some embodiments,the threshold voltage may be a static value. In some embodiments, thethreshold voltage may be a dynamic value based on the load demand. Insome embodiments, the AC electrical power imported by a bi-directionalAC/DC inverter from the AC electrical power bus may include ACelectrical power exported by another bi-directional AC/DC inverter tothe AC electrical power bus.

In some embodiments, the microgrid system may be a standalone fuel cellmicrogrid system, such that the fuel cell microgrid system is notelectrically connected to an electrical power utility grid. In someembodiments, the microgrid system may be electrically connectable orselectively electrically connectable to an electrical power utilitygrid. In some embodiments, the AC electrical power exported by abi-directional AC/DC inverter to the AC electrical power bus may beprovided to the electrical power utility grid. In some embodiments, theAC electrical power imported by a bi-directional AC/DC inverter from theAC electrical power bus may include AC electrical power provided by theelectrical power utility grid. In some embodiments, the AC electricalpower exported by a bi-directional AC/DC inverter to the AC electricalpower bus may be provided to an auxiliary electrical power storage unit,and the AC electrical power imported by a bi-directional AC/DC inverterfrom the AC electrical power bus may be provided by the auxiliaryelectrical power storage unit. In some embodiments, excess AC electricalpower on the AC electrical power bus may be dissipated by an electricalpower dissipation unit, such as a resistor load.

FIG. 1 illustrates an example of one DC electrical power source, whichcomprises modular fuel cell system that is more fully described in U.S.Pat. No. 8,440,362, incorporated herein by reference for descriptions ofthe modular fuel cell system. The modular system may contain modules andcomponents described above as well as in U.S. Pat. No. 9,190,693, whichis incorporated herein by reference for descriptions of the modular fuelcell system. The modular design of the fuel cell system enclosure 10provides flexible system installation and operation.

The modular fuel cell system enclosure 10 includes a plurality of powermodule housings 12 (containing a fuel cell power module components), oneor more fuel input (i.e., fuel processing) module housings 16, and oneor more power conditioning (i.e., electrical output) module housings 18.For example, the system enclosure may include any desired number ofmodules, such as 2-30 power modules, for example 6-12 power modules.FIG. 1 illustrates a system enclosure 10 containing six power modules(one row of six modules stacked side to side), one fuel processingmodule, and one power conditioning module, on a common base 20. Eachmodule may comprise its own cabinet or housing. Alternatively, the powerconditioning and fuel processing modules may be combined into a singleinput/output module located in one cabinet or housing 14. For brevity,each housing 12, 14, 16, 18 will be referred to as “module” below.

While one row of power modules 12 is shown, the system may comprise morethan one row of modules 12. For example, the system may comprise tworows of power modules stacked back to back.

Each power module 12 is configured to house one or more hot boxes 13.Each hot box contains one or more stacks or columns of fuel cells (notshown for clarity), such as one or more stacks or columns of solid oxidefuel cells having a ceramic oxide electrolyte separated by conductiveinterconnect plates. Other fuel cell types, such as PEM, moltencarbonate, phosphoric acid, etc. may also be used.

The modular fuel cell system enclosure 10 also contains one or moreinput or fuel processing modules 16. This module 16 includes a cabinetwhich contains the components used for pre-processing of fuel, such asdesulfurizer beds. The fuel processing modules 16 may be designed toprocess different types of fuel. For example, a diesel fuel processingmodule, a natural gas fuel processing module, and an ethanol fuelprocessing module may be provided in the same or in separate cabinets. Adifferent bed composition tailored for a particular fuel may be providedin each module. The processing module(s) 16 may processes at least oneof the following fuels selected from natural gas provided from apipeline, compressed natural gas, methane, propane, liquid petroleumgas, gasoline, diesel, home heating oil, kerosene, JP-5, JP-8, aviationfuel, hydrogen, ammonia, ethanol, methanol, syn-gas, bio-gas, bio-dieseland other suitable hydrocarbon or hydrogen containing fuels. If desired,a reformer 17 may be located in the fuel processing module 16.Alternatively, if it is desirable to thermally integrate the reformer 17with the fuel cell stack(s), then a separate reformer 17 may be locatedin each hot box 13 in a respective power module 12. Furthermore, ifinternally reforming fuel cells are used, then an external reformer 17may be omitted entirely.

The modular fuel cell system enclosure 10 also contains one or morepower conditioning modules 18. The power conditioning module 18 includesa cabinet which contains the components for converting the fuel cellstack generated DC power to AC power, electrical connectors for AC poweroutput to the grid, circuits for managing electrical transients, asystem controller (e.g., a computer or dedicated control logic device orcircuit). The power conditioning module 18 may be designed to convert DCpower from the fuel cell modules to different AC voltages andfrequencies. Designs for 208V, 60 Hz; 480V, 60 Hz; 415V, 50 Hz and othercommon voltages and frequencies may be provided.

The fuel processing module 16 and the power conditioning module 18 maybe housed in one input/output cabinet 14. If a single input/outputcabinet 14 is provided, then modules 16 and 18 may be located vertically(e.g., power conditioning module 18 components above the fuel processingmodule 16 desulfurizer canisters/beds) or side by side in the cabinet14.

As shown in an example embodiment in FIG. 1 , one input/output cabinet14 is provided for one row of six power modules 12, which are arrangedlinearly side to side on one side of the input/output module 14. The rowof modules may be positioned, for example, adjacent to a building forwhich the system provides power (e.g., with the backs of the cabinets ofthe modules facing the building wall). While one row of power modules 12is shown, the system may include more than one row of modules 12. Forexample, as noted above, the system may include two rows of powermodules stacked back to back.

Each of the power modules 12 and input/output modules 14 include a door30 (e.g., hatch, access panel, etc.) to allow the internal components ofthe module to be accessed (e.g., for maintenance, repair, replacement,etc.). According to one embodiment, the modules 12 and 14 are arrangedin a linear array that has doors 30 only on one face of each cabinet,allowing a continuous row of systems to be installed abutted againsteach other at the ends. In this way, the size and capacity of the fuelcell enclosure 10 can be adjusted with additional modules 12 or 14 andbases 20 with minimal rearranging needed for existing modules 12 and 14and bases 20. If desired, the door 30 to module 14 may be on the siderather than on the front of the cabinet.

FIG. 2 illustrates a plan view of a fuel cell system hotbox 13 includinga fuel cell stack or column 40. The hotbox 13 is shown to include thefuel cell stack or column 40. However, the hotbox 13 may include two ormore of the stacks or columns 40. The stack or column 40 may include theelectrically connected fuel cells 45 stacked on one another, with theinterconnects 50 disposed between the fuel cells 45. The first and lastfuel cells 45 in the stack or column are disposed between a respectiveend plate 60 and interconnect 50. The end plates 60 are electricallyconnected to electrical outputs of the fuel cell stack or column 40. Thehotbox 13 may include other components, such as fuel conduits, airconduits, seals, electrical contacts, etc., and may be incorporated intoa fuel cell system including balance of plant components. The fuel cells45 may be solid oxide fuel cells containing a ceramic electrolyte, suchas yttria stabilized zirconia (YSZ) or scandia stabilized zirconia(SSZ), an anode electrode, such as a nickel-YSZ, a Ni-SSZ or anickel-samaria doped ceria (SDC) cermet, and a cathode electrode, suchas lanthanum strontium manganite (LSM)). The interconnects 50 and/or endplates 60 may comprise any suitable gas impermeable and electricallyconductive material, such as a chromium-iron alloy, such as an alloycontaining 4 to 6 wt % iron and balance chromium. The interconnects 50electrically connect adjacent fuel cells 45 and provide channels forfuel and air to reach the fuel cells 45.

Fuel cell systems, such as modular fuel cell system enclosure 10, mayinclude and/or be augmented by various pieces of support equipment.Support equipment may include various auxiliary equipment and systems tosupport the operation of the fuel cell system. Support equipment mayvary based on constraints and/or features at a site where the fuel cellsystem is installed. As non limiting examples, support equipment mayinclude, fuel support equipment, air support equipment, and/orventilation support equipment. One type of fuel support equipment mayinclude equipment configured to control supply and/or exhaust fuelpressure in the fuel cell system, such as a fuel blower or pump tosupply fuel to, recycle fuel/exhaust in, and/or exhaust fuel from thefuel cell system. Another type of fuel support equipment may beconfigured to process fuel for the fuel cell system, such as a fuelpre-heater, exhaust scrubber, etc. Other types of fuel support equipmentmay also be used. One type of air support equipment may be air supplyequipment configured to provide air into the fuel cell system and/orexhaust air from the fuel cell system, such as blowers or fans toprovide air to and/or exhaust air from a fuel cell cathode, an anodetail gas oxidizer (ATO), an air heat exchanger, a CPOx reactor, etc.Other types of air support equipment may also be used. One type ofventilation support equipment may include equipment configured toventilate from and/or circulate air in portions of housings external ofthe hot box (e.g., portions within modular fuel cell system enclosure 10but external of the hot box 13 itself), such as a ventilation fan toblow air from within the enclosure 10 out of the enclosure 10 tomaintain an acceptable enclosure 10 pressure. Other types of ventilationsupport equipment may also be used. Support equipment, especiallysupport equipment including electric motors may require AlternatingCurrent (AC) power, for example one, two, or three phase AC power, foroperation.

FIGS. 3-5 illustrate multiple embodiments of a microgrid system, such asa fuel cell microgrid system, having bi-directional AC/DC inverters. Amicrogrid system may include a variety of components, including anynumber and combination of power modules 12, power module clusters 300,bi-directional AC/DC inverters 302, uninterruptable power modules 304,AC electrical power busses 306, DC electrical power busses 308, and loadelectrical power busses 310. The power modules 12 may comprise fuel cellpower modules described above, and/or any other type of DC power sourcepower modules, such as solar cell power modules, etc. The microgridsystem may include any number of control devices (herein also referredto as controllers) 314 configured to receive data signals from and sendcontrol signals to any number and combination of the components of themicrogrid system via any number “R” of wired and/or wireless connectionsA1-AR. The control device(s) 314 may be any form of programmablecomputing device or system, such as a server or system control device,which may be configured to perform operations of various embodiments,including operations of the methods 600, 700, 800 described herein withreference to FIGS. 6-8 . The microgrid system may be electricallyconnectable to an AC load 312 configured to operate using AC electricalpower. Each uninterruptable power module 304 may be configured toprovide the same amount of electrical power to the AC load 312 via aload electrical power bus 310. In some embodiments, the microgrid systemmay be electrically connected to an AC electrical power source, such asan electrical power utility grid 316. For simplicity, a fuel cellmicrogrid will be described below which includes fuel cell power modules12. FIGS. 3-5 illustrate various embodiments that are meant to beillustrative examples and not limiting of the scope of the claims.

A fuel cell microgrid system may include any number “M” of power moduleclusters 300, such as 2 to 20, e.g., 2 to 6. Each power module cluster300 may include any number of fuel cell power modules 12 that may beconfigured as described herein with reference to FIG. 1 . In someembodiments, each power module cluster 300 may include any number “N” ofpower modules 12, such as 1 to 12, e.g., 5 to 10. In some embodiments,the number of power modules 12 included in a power module cluster 300may vary between the various power module clusters 300. The powermodules 12 of a single power module cluster 300 may be insufficient togenerate electrical power to satisfy at least normal electrical powerdemands of the AC load 312. The number of power modules 12 divided amongmultiple power module clusters 300 in the fuel cell microgrid system maybe at least as many power modules 12 necessary to generate sufficienttotal electrical power to satisfy at least normal electrical powerdemands of the AC load 312. Similarly, the number of power modules 12divided among multiple power module clusters 300 in the fuel cellmicrogrid system may be at least as many power modules 12 necessary togenerate an equal amount of electrical power from each power modulecluster 300 to satisfy at least normal electrical power demands of theAC load 312. In various embodiments, the number of power modules 12 mayinclude any number of redundant power modules 12 so that in case ofreduced or no electrical output from at least one power module 12, aredundant power module 12 may be used to continue supply of theelectrical power demand of the AC load 312.

A power module cluster 300 may be electrically connected to a respectiveDC electrical power bus 308 and configured to supply DC electrical powerto the DC electrical power bus 308. The power module cluster 300 may beconfigured in a manner in which, under normal operation, such as withinexpected degradation parameters and/or without failure of a power module12, the power module cluster 300 may provide at least a portion of theelectrical power required to satisfy the electrical power demand of theAC load 312. Preferably, the power module cluster 300 may be configuredin a manner in which, under normal operation, the power module cluster300 may provide sufficient electrical power for a respectiveuninterruptable power module 304 which is electrically connected to thepower module cluster 300 via the DC electrical power bus 308, to providea same amount electrical power to the AC load 312 as the otheruninterruptable power modules 304 of the fuel cell microgrid system.

An uninterruptable power module 304 may be electrically connected to arespective power module cluster 300 via a respective DC electrical powerbus 308 and electrically connectable to the AC load 312 via the loadelectrical power bus 310. The uninterruptable power module 304 may beconfigured as or to include a DC/AC inverter. The uninterruptable powermodule 304 may be configured to invert a DC electrical power receivedfrom an electrical power source (e.g., from the power module cluster(s)300) to an AC electrical power. The uninterruptable power module 304 maycontain unidirectional DC/AC inverter, configured to receive DCelectrical power at an input end and to supply AC electrical power at anoutput end. In some embodiments, the electrical power source may includeany number and combination of a power module cluster 300 and/or a powermodule 12, an electrical power utility grid 316, an auxiliary electricalpower storage unit 500 (shown in FIG. 5 ) as described further hereinwith reference to FIGS. 3-5 . The uninterruptable power module 304 maybe electrically connected at the input end to any number and combinationof electrical power sources via the DC electrical power bus 308. Theuninterruptable power module 304 may be electrically connectable at theoutput end to the AC load 312 via the load electrical power bus 310. ADC electrical power received by the uninterruptable power module 304from one or more electrical power sources may be inverted by theuninterruptable power module 304 and supplied to the AC load 312 as anAC electrical power. In some embodiments, the uninterruptable powermodule 304 may be configured to supply a designated amount of electricalpower having a given voltage and/or current, for example, based onelectrical power configuration of the AC load 312 and/or the electricalpower demand of the AC load 312. In some embodiments, eachuninterruptable power module 304 of the fuel cell microgrid system maybe configured to receive a same amount of input DC electrical power andoutput a same amount of output AC electrical power. A fuel cellmicrogrid system may include any number “Q” of uninterruptable powermodules 304, each disposed between an electrical power source and the ACload 312. In some embodiments, a fuel cell microgrid system may includea one-to-one ratio of power module clusters 300 to uninterruptable powermodules 304, such that Q=M.

A bi-directional AC/DC inverter 302 may be selectively electricallyconnectable to a respective power module cluster 300 via a respective DCelectrical power bus 308 and selectively electrically connectable toother bi-directional AC/DC inverters 302 via an AC electrical power bus306. The bi-directional AC/DC inverter 302 may be configured to rectifyan AC electrical power received at an AC end from an electrical powersource to a DC electrical power, and invert a DC electrical powerreceived at a DC end from the power module cluster 300 and/or a powermodule 12 to an AC electrical power. In some embodiments, the electricalpower source which provides the AC electrical power through the ACelectrical power bus may include any number and combination of otherpower module cluster(s) 300 and/or other power module(s) 12 (i.e., whichare electrically connected to the respective bi-directional AC/DCconverter 302 via the AC electrical power bus 306 and which are notconnected to the respective bi-directional AC/DC converter 302 via theDC electrical power bus 308), an electrical power utility grid 316,and/or an auxiliary electrical power storage unit 500 as describedfurther herein with reference to FIGS. 3-5 . The bi-directional AC/DCinverter 302 may be selectively electrically connectable at the AC endto any number and combination of electrical power sources via the ACelectrical power bus 306. The bi-directional AC/DC inverter 302 may beselectively electrically connectable at the DC end to the power modulecluster 300 and/or the power module 12 via the DC electrical power bus308. An AC electrical power received by the bi-directional AC/DCinverter 302 from one or more electrical power sources may be rectifiedby the bi-directional AC/DC inverter 302 and supplied to its respectiveDC electrical power bus 308 as a DC electrical power. A DC electricalpower received by the bi-directional AC/DC inverter 302 from the powermodule cluster 300 and/or the power module 12 via its respective DCelectrical power bus 308 may be inverted by the bi-directional AC/DCinverter 302 and supplied to the AC electrical power bus 306 as an ACelectrical power. A fuel cell microgrid system may include any number“P” of bi-directional AC/DC inverters 302, each disposed between the ACelectrical power bus 306 and its respective DC electrical power bus 308.In some embodiments, a fuel cell microgrid system may include aone-to-one ratio of power module clusters 300 to bi-directional AC/DCinverters 302, such that P=M.

The bi-directional AC/DC inverter 302 may be configured to export DCelectrical power (i.e., invert DC electrical power to AC electricalpower) in response to an amount of electrical power, such as a measuredvoltage and/or current, on the DC electrical power bus 308 exceeding aDC electrical power threshold, such as a voltage and/or currentthreshold. The bi-directional AC/DC inverter 302 may be configured toimport AC electrical power (i.e., rectify AC electrical power to DCelectrical power) in response to an amount of electrical power on the DCelectrical power bus 308 falling short of the DC electrical powerthreshold. In some embodiments, the DC electrical power threshold may bea voltage and/or current at which equal electrical power supplied fromeach of the power module clusters 300 may satisfy the load demand of theAC load 312. Therefore, DC electrical power on the DC electrical powerbus 308 exceeding the DC electrical power threshold may be electricalpower in excess of what the uninterruptable power module 304 may outputto the AC load 312 via bus 310. DC electrical power on the DC electricalpower bus 308 falling short of the DC electrical power threshold may beelectrical power in deficit of what the uninterruptable power module 304may output to the AC load 312 via bus 310. In some embodiments, the DCelectrical power threshold may be a static value based on the electricalconfiguration of the AC load 312. In some embodiments, the DC electricalpower threshold may be a dynamic value based on the load demand of theAC load 312.

The controller 314 may directly measure and/or interpret receivedsignals as the voltage and/or current on the DC electrical power bus308. For example, the controller 314 may directly measure and/orinterpret received signals as the voltage and/or current on the DCelectrical power bus 308 at and/or from the bi-directional AC/DCinverter 302. The controller 314 may further compare the voltage and/orcurrent on the DC electrical power bus 308 to the DC electrical powerthreshold. In response to determining from the comparison that thevoltage and/or current on the DC electrical power bus 308 exceeds the DCelectrical power threshold, the controller 314 may signal and/or controlthe bi-directional AC/DC inverter 302 to export DC electrical power. Inresponse to determining from the comparison that the voltage and/orcurrent on the DC electrical power bus 308 falls short the DC electricalpower threshold, the controller 314 may signal and/or control thebi-directional AC/DC inverter 302 to import AC electrical power. Assuch, when DC electrical power on the DC electrical power bus 308 is inexcess of what the uninterruptable power module 304 may output to the ACload 312 via bus 310, the excess amount electrical power may be outputto the AC electrical power bus 306 from the DC electrical power bus 308.When the DC electrical power on the DC electrical power bus 308 is indeficit of what the uninterruptable power module 304 may output to theAC load 312 via bus 310, the deficit amount of electrical power may beinput to the DC electrical power bus 308 from the AC electrical powerbus 306.

The control of one or more bi-directional AC/DC inverters 302 mayprovide sufficient DC electrical power to each of the uninterruptablepower modules 304 for each of the uninterruptable power modules 304 toprovide an equal amount of AC electrical power to satisfy the loaddemand of the AC load 312. As such, imbalances in the outputs of theuninterruptable power modules 304 may be balanced by remedying deficitsof DC electrical power on any of the DC electrical power busses 308 byimporting AC electrical power so that each of the uninterruptable powermodules 304 may provide the equal amount of AC electrical power.

The DC electrical power bus 308 may be configured as a common electricalconduit for respective groups of a bi-directional AC/DC inverter 302, apower module cluster 300, and an uninterruptable power module 304. TheDC electrical power bus 308 may be configured to transmit DC electricalpower between the bi-directional AC/DC inverter 302, the power modulecluster 300, and the uninterruptable power module 304 of a respectivegroup. The DC electrical power bus 308 may electrically connect the DCend of each of the bi-directional AC/DC inverter 302 and the input endof the uninterruptable power module 304.

The AC electrical power bus 306 may be configured as a common electricalconduit for the bi-directional AC/DC inverters 302. The AC electricalpower bus 306 may be configured to transmit AC electrical power betweenthe bi-directional AC/DC inverters 302. In some embodiments, the ACelectrical power bus 306 may be further configured as a commonelectrical conduit for AC electrical power transmission between thebi-directional AC/DC inverters 302 and the electrical power utility grid316. In some embodiments, the AC electrical power bus 306 may be furtherconfigured as a common electrical conduit for AC electrical powertransmission between the bi-directional AC/DC inverters 302, theelectrical power utility grid 316, the auxiliary power storage unit 500,and/or an electrical power dissipation unit 502 shown in FIG. 5 . The ACelectrical power bus 306 may electrically connect the AC ends of thebi-directional AC/DC inverters 302. In some embodiments, the ACelectrical power bus 306 may electrically connect the AC ends of thebi-directional AC/DC inverters 302 and the electrical power utility grid316, the auxiliary power storage unit 500, and/or the electrical powerdissipation unit 502.

The load electrical power bus 310 may be configured as a commonelectrical conduit for the uninterruptable power modules 304. The loadelectrical power bus 310 may be configured to transmit AC electricalpower between the uninterruptable power modules 304 and the AC load 312.The load electrical power bus 310 may electrically connect the AC end ofeach of the uninterruptable power modules 304 and the AC load 312.

An AC load 312 may be configured to consume electrical power from thefuel cell microgrid system. In various embodiments, electrical power maybe provided to a fuel cell microgrid system by any number andcombination of a power modules 12 and power module clusters 300. A fuelcell microgrid system may provide electrical power to any number of ACloads 312. A voltage and/or amperage of electrical power required by anAC load 312 may be an electrical power demand of the AC load 312 on thefuel cell microgrid system. In some embodiments, multiple AC loads 312may require voltage and/or amperage of electrical power to be withinspecific requirements, and combined these requirements may present anelectrical power demand of the AC load 312 on the fuel cell microgridsystem.

In some embodiments, the controller 314 may be a central controller 314configured to communicatively connect to any number and combination ofcomponents of the fuel cell microgrid system. In some embodiments, thecontroller 314 may be multiple dispersed controllers 314 configured tocommunicatively connect to any number and combination of components ofthe fuel cell microgrid system. In some embodiments, the controller 314may be a standalone controller of the fuel cell microgrid system. Insome embodiments, the controller 314 may be an integrated controller ofany number and combination of components of the fuel cell microgridsystem. Any number and combination of the forgoing configurations of thecontroller 314 may be implemented in a fuel cell microgrid system.

The examples illustrated in FIGS. 3-5 are described for illustrativepurposes and are not meant to limit the scope of the claims anddisclosures made herein. These examples are described herein in terms oftwo power module clusters 300 (a first power module cluster 300, e.g.,power module cluster 1 in FIGS. 3-5 , and a second power module cluster,e.g., power module cluster M in FIGS. 3-5 ) and their respective DCelectrical power busses 308 (a first DC electrical power bus 308 and asecond electrical power bus 308), and two bi-directional AC/DC inverters302 (a first bi-directional AC/DC inverter 302, e.g., bi-directionalAC/DC inverter 1 in FIGS. 3-5 , and a second bi-directional AC/DCinverter 302, e.g., bi-directional AC/DC inverter P in FIGS. 3-5 ).However, the examples illustrated and described herein are applicable toany number greater than two power module clusters 300 (e.g., three ormore clusters 300) and their respective DC electrical power busses 308(e.g., three or more buses 308), and/or bi-directional AC/DC inverters302 (e.g., three or more inverters 302).

FIG. 3 illustrates an example of a fuel cell microgrid system havingbi-directional AC/DC inverters 302. The fuel cell microgrid system mayinclude at least a first bi-directional AC/DC inverter 302 and at leasta second bi-directional AC/DC inverter 302, each electrically connectedbetween the AC electrical power bus 306 and a respective DC electricalpower bus 308. In such embodiments, each bi-directional AC/DC inverter302 may be configured to export DC electrical power in response to anamount of electrical power on the respective DC electrical power bus 308exceeding the DC electrical power threshold. Each bi-directional AC/DCinverter 302 may be configured to import AC electrical power in responseto an amount of electrical power on the respective DC electrical powerbus 308 falling short of the DC electrical power threshold.

As such, as long as one AC/DC inverter 302 is set to export DCelectrical power, there may be AC electrical power available on the ACelectrical power bus 306 for another AC/DC inverter 302 to import ACelectrical power. For example, the first bi-directional AC/DC inverter302 may configured to export DC electrical power from the first DCelectrical power bus 308 in response to DC electrical power on the firstDC electrical power bus 308 exceeding the DC electrical power threshold.The first bi-directional AC/DC inverter 302 may receive DC electricalpower at a DC end from the first DC electrical power bus 308, invert theDC electrical power to AC electrical power, and output AC electricalpower at an AC end to the AC electrical power bus 306. The firstbi-directional AC/DC inverter 302 may remain configured to export DCelectrical power as long as the DC electrical power on the first DCelectrical power bus 308 remains higher than the DC electrical powerthreshold.

A second power module cluster 300 (e.g., power module cluster M in FIG.3 ) having a degraded and/or failed power module 12 (e.g., degradedpower module 1), may not be able the generate and output to the secondDC electrical power bus 308 sufficient DC electrical power to meetand/or exceed the DC electrical power threshold. In response to DCelectrical power on the second DC electrical power bus 308 falling shortof the DC electrical power bus threshold, the second bi-directionalAC/DC inverter 302 (e.g., inverter P) may be configured to import ACelectrical power from the AC electrical power bus 306. The secondbi-directional AC/DC inverter 302 may receive AC electrical power at anAC end from the AC electrical power bus 306, rectify the AC electricalpower to DC electrical power, and output DC electrical power at a DC endto the second DC electrical power bus 308. The second bi-directionalAC/DC inverter 302 may remain configured to import AC electrical poweras long as the DC electrical power on the second DC electrical power bus308 remains below the DC electrical power threshold.

In some embodiments, the fuel cell microgrid system may be electricallyconnected to an electrical power utility grid 316 via the AC electricalpower bus 306. When configured to import AC electrical power from the ACelectrical power bus 306, the second bi-directional AC/DC inverter 302may draw sufficient AC electrical power from the AC electrical power bus306 to provide sufficient DC electrical power to the second DCelectrical power bus 308 so that the DC electrical power on the secondDC electrical power bus 308 no longer falls short of the DC electricalpower threshold. In some situations, the DC electrical power exported bythe first bi-directional AC/DC inverter 302 (e.g., power to inverter 1from power module cluster 1) and provided as AC electrical power to theAC electrical power bus 306 may be sufficient AC electrical power tosatisfy the needs of the second bi-directional AC/DC inverter 302 andsecond DC electrical power bus 308. In some situations, the DCelectrical power exported by the first bi-directional AC/DC inverter 302and provided as AC electrical power to the AC electrical power bus 306may be insufficient AC electrical power to satisfy the needs of thesecond bi-directional AC/DC inverter 302 and second DC electrical powerbus 308. In such situations, the second bi-directional AC/DC inverter302 may supplement the amount of AC electrical power imported from theAC electrical power bus 306 and provided by the first bi-directionalAC/DC inverter 302 with AC electrical power from the electrical powerutility grid 316 via the AC electrical power bus 306. The secondbi-directional AC/DC inverter 302 may draw any amount of AC electricalpower from the electrical power utility grid 316 via the AC electricalpower bus 306. For example, the amount of AC electrical power drawn fromthe electrical power utility grid 316 may be a difference between anamount of AC electrical power provided to the AC electrical power bus306 by the first bi-directional AC/DC inverter 302 and an amount ofelectrical power needed by the second bi-directional AC/DC inverter 302.In a further example, the amount of AC electrical power drawn from theelectrical power utility grid 316 may be all of an amount of ACelectrical power needed by the second bi-directional AC/DC inverter 302.For further example, the amount of AC electrical power drawn from theelectrical power utility grid 316 and from AC electrical power providedby the first bi-directional AC/DC inverter 302 may be configured as aset ratio of or set amount of AC electrical power from the electricalpower utility grid 316 and the first bi-directional AC/DC inverter 302.

FIG. 4 illustrates an example of a fuel cell microgrid system havingbi-directional inverters 302 and configured for selective electricalpower utility grid isolation. In addition to the descriptions of theexamples illustrated in FIG. 3 , the fuel cell microgrid system mayinclude a selective electrical connector 400 configured to selectivelyelectrically connect the fuel cell microgrid system via the ACelectrical power bus 306 to the electrical power utility grid 316. Insome embodiments, the selective electrical connector 400 may beconfigured to electrically connect the AC electrical power bus 306 tothe electrical power utility grid 316 when AC electrical power isavailable from the electrical power utility grid 316. The selectiveelectrical connector 400 may be configured to electrically disconnectthe AC electrical power bus 306 from the electrical power utility grid316 when AC electrical power is not available from the electrical powerutility grid 316. For example, the selective electrical connector 400may be configured to electrically connect the AC electrical power bus306 to the electrical power utility grid 316 when AC electrical power isavailable from the electrical power utility grid 316 during a gridevent, such as a power outage. The selective electrical connector 400may be any type of electromechanical or electronic component (e.g.,relay or solid state switch) configured to allow and prevent the flow ofelectrical power between a first end of the selective electricalconnector 400 and a second end of the selective electrical connector400.

In some embodiment, the selective electrical connector 400 may becontrolled by the controller 314. The controller 314 may directlymeasure and/or interpret received signals as the voltage and/or currentavailable from the electrical power utility grid 316, for example, atand/or from the selective electrical connector 400. The controller 314may determine whether to open or close the selective electricalconnector 400, selectively electrically connecting or disconnecting theAC electrical power bus 306 and the electrical power utility grid 316.In some embodiments, the controller 314 may selectively electricallydisconnect the AC electrical power bus 306 and the electrical powerutility grid 316 when the controller 314 measures and/or interprets thatthere is no or negligible AC electrical power available from theelectrical power grid utility 316. In some embodiments, the controller314 may selectively electrically connect the AC electrical power bus 306and the electrical power utility grid 316 when the controller 314measures and/or interprets that there is more than no or negligible ACelectrical power available from the electrical power grid utility 316.

FIG. 5 illustrates an example of a fuel cell microgrid system havingbi-directional inverters 302 and auxiliary electrical power storageand/or electrical power dissipation. In addition to the descriptions ofthe examples illustrated in FIGS. 3 and 4 , the fuel cell microgridsystem may include any number and combination of auxiliary electricalpower storage units 500 and/or electrical power dissipation units 502.In some embodiments, an auxiliary electrical power storage unit 500 maybe any sort of electrical, electrochemical, electromechanical, and/orthermal energy storage unit. For example, an auxiliary electrical powerstorage unit 500 may be a battery or supercapacitor. In someembodiments, an electrical power dissipation unit 502 may be any sort ofelectrical, electrochemical, electromechanical, and/or thermal energydissipation unit. For example, an auxiliary electrical power storageunit 500 may be a resistor load.

In situations where the second bi-directional AC/DC inverter 302 is setto import AC electrical power from the AC electrical bus 306, there maybe more AC electrical power on the AC electrical power bus 306 than thesecond bi-directional AC/DC inverter 302 needs to draw. In situationswhere the second bi-directional AC/DC inverter 302 is not set to importAC electrical power from the AC electrical power bus 306, there maystill be AC electrical power on the AC electrical power bus 306. Theexcess AC electrical power on the AC electrical power bus 306 may beprovided to the AC electrical power bus 306 by the first bi-directionalAC/DC inverter 302 set to export DC electrical power from the first DCelectrical power bus 308 and/or the electrical power utility grid 316.

An auxiliary electrical power storage unit 500 may be electricallyconnected to the AC electrical power bus 306. In situations where acharge of the auxiliary electrical power storage unit 500 falls short ofa charge capacity threshold, the auxiliary electrical power storage unit500 may charge using the excess AC electrical power on the AC electricalpower bus 306. In situations where the charge of the auxiliaryelectrical power storage unit 500 meets or exceeds the charge capacitythreshold, the auxiliary electrical power storage unit 500 may notcharge using the excess AC electrical power on the AC electrical powerbus 306. In situations where the second bi-directional AC/DC inverter302 is set to import AC electrical power from the AC electrical bus 306and there is insufficient AC electrical power on the AC electrical powerbus 306 to satisfy the need for AC electrical power of the secondbi-directional AC/DC inverter 302, the auxiliary electrical powerstorage unit 500 may output AC electrical power to the AC electricalpower bus 306. In some embodiments, the auxiliary electrical powerstorage unit 500 may include a bi-directional AC/DC inverter (not shown)configured to rectify AC electrical power received at an AC end from theAC electrical power bus 306 and provide DC electrical power at a DC endto the auxiliary electrical power storage unit 500. The bi-directionalAC/DC inverter may be further configured to convert DC electrical powerreceived at the DC end from the auxiliary electrical power storage unit500 and provide AC electrical power at the AC end to the AC electricalpower bus 306.

In some embodiment, the auxiliary electrical power storage unit 500 maybe controlled by the controller 314. The controller 314 may directlymeasure and/or interpret received signals as the voltage and/or currentavailable from the AC electrical power bus 306 and the auxiliaryelectrical power storage unit 500, for example, at and/or from theauxiliary electrical power storage unit 500. The controller 314 mayfurther compare the voltage and/or current of the auxiliary electricalpower storage unit 500 to the charge capacity threshold. In response todetermining from the comparison that the voltage and/or current of theauxiliary electrical power storage unit 500 meets or exceeds the chargecapacity threshold when there is a deficit of AC electrical power on theAC electrical power bus 306, the controller 314 may signal and/orcontrol the auxiliary electrical power storage unit 500 to export DCelectrical power. In response to determining from the comparison thatthe voltage and/or current of the auxiliary electrical power storageunit 500 falls short of the charge capacity threshold when there isexcess AC electrical power on the AC electrical power bus 306, thecontroller 314 may signal and/or control the auxiliary electrical powerstorage unit 500 to import AC electrical power.

The electrical power dissipation unit 502 may be electrically connectedto the AC electrical power bus 306. In situations where the selectiveelectrical connector 400 is open (i.e., the AC electrical power bus 306is not electrically connected to the power grid 316) and there is excessAC electrical power on the AC electrical power bus 306 (i.e., in excessof the power demand of the auxiliary electrical power storage unit 500and/or the bi-directional AC/DC inverters 302), the excess AC electricalpower is dissipated by the electrical power dissipation unit 502.

In some embodiments, the electrical power dissipation unit 502 may be apassive device configured to dissipate AC electrical power received fromthe AC electrical power bus 306. In some embodiment, the electricalpower dissipation unit 502 may be an active device controlled by thecontroller 314. The controller 314 may directly measure and/or interpretreceived signals as the voltage and/or current available from the ACelectrical power bus 306, for example, at and/or from the electricalpower dissipation unit 502. In response to excess AC electrical power onthe AC electrical power bus 306, the controller 314 may control and/orsignal the electrical power dissipation unit 502 to dissipate the excessAC electrical power.

FIG. 6 illustrates a method 600 for managing a fuel cell microgridsystem of FIGS. 4 and/or 5 according to various embodiments. The method600 may be implemented using one or more controllers 314 configured toreceive signals from and/or send control signals to any number orcombination of bi-directional AC/DC inverters 302, AC electrical powerbusses 306, and/or selective electrical connector 400. In order toencompass the alternative configurations provided in variousembodiments, the hardware implementing the method 600 is referred toherein as a “control device.”

In determination block 602, the control device may determine whether ACelectrical power is available from an electrical power utility grid 316.The control device may directly measure and/or interpret receivedsignals as the voltage and/or current available from the electricalpower utility grid 316, for example, at and/or a from bi-directionalAC/DC inverter 302, an AC electrical power bus 306, and/or a selectiveelectrical connector 400. If the control device measures and/orinterprets that there is no or negligible AC electrical power availablefrom the electrical power utility grid 316, the control devicedetermines that there is not AC electrical power available from theelectrical power grid utility 316. If the control device measures and/orinterprets that there is more than no or negligible AC electrical poweravailable from the electrical power grid utility 316, then the controldevice determines that there is AC electrical power available from theelectrical power grid utility 316.

In response to determining that there is not AC electrical poweravailable from the electrical power grid utility 316 (i.e.,determination block 602=“No”), the control device may open the selectiveelectrical connector 400 in optional block 604. Opening the selectiveelectrical connector 400 may selectively electrically disconnect a fuelcell microgrid system from the electrical power utility grid 316. Forexample, opening the selective electrical connector 400 may selectivelyelectrically disconnect the AC electrical power bus 306 of the fuel cellmicrogrid system from the electrical power utility grid 316. The controldevice may control and/or signal to the selective electrical connector400 to open.

In response to determining that there is not AC electrical poweravailable from the electrical power grid utility 316 (i.e.,determination block 602=“No”), or following opening the selectiveelectrical connector 400 in optional block 604, the control device mayimplement determination block 702 of the method 700 described furtherherein with reference to FIG. 7 .

In response to determining that there is AC electrical power availablefrom the electrical power grid utility 316 (i.e., determination block602=“Yes”), the control device may close the selective electricalconnector 400 in optional block 606. Closing the selective electricalconnector 400 may selectively electrically connect the fuel cellmicrogrid system to the electrical power utility grid 316. For example,closing the selective electrical connector 400 may selectivelyelectrically connect the AC electrical power bus 306 of the fuel cellmicrogrid system to the electrical power utility grid 316. The controldevice may control and/or signal to the selective electrical connector400 to close.

In response to determining that there is AC electrical power availablefrom the electrical power grid utility 316 (i.e., determination block602=“Yes”), or following closing the selective electrical connector 400in optional block 606, the control device may implement determinationblock 702 of the method 800 described further herein with reference toFIG. 8 .

FIG. 7 illustrates a method 700 for managing a fuel cell microgridsystem in grid independent mode (i.e., when the selective electricalconnector 400 is open or if the microgrid is not electrically connectedto electrical power utility grid) according to various embodiments. Themethod 700 may be implemented using one or more controllers 314configured to receive signals from and/or send control signals to anynumber or combination of bi-directional AC/DC inverters 302,uninterruptable power modules 304, AC electrical power busses 306,and/or DC electrical power busses 308. In order to encompass thealternative configurations provided in various embodiments, the hardwareimplementing the method 700 is referred to herein as a “control device.”

In determination block 702, the control device may determine whether theDC electrical power, i.e., voltage and/or current, on a DC electricalpower bus 308 falls short of a DC electrical power threshold, such as avoltage and/or current threshold. In some embodiments, the DC electricalpower threshold may be a voltage and/or current at which equalelectrical power supplied from each of the power module clusters 300 maysatisfy the load demand of the AC load 312. The control device maydirectly measure and/or interpret received signals as the voltage and/orcurrent on the DC electrical power bus 308. For example, the controldevice may directly measure and/or interpret received signals as thevoltage and/or current on the DC electrical power bus 308 at and/or froma bi-directional AC/DC inverter 302. The control device may furthercompare the voltage and/or current on the DC electrical power bus 308 tothe DC electrical power threshold.

In response to determining that the DC electrical power on the DCelectrical power bus 308 falls short of the DC electrical powerthreshold (i.e., determination block 702=“Yes”), the control device mayset the bi-directional AC/DC inverter 302 to import AC electrical powerfrom the AC electrical power bus 306 in block 704. The control devicemay signal and/or control the bi-directional AC/DC inverter 302 toimport AC electrical power.

In block 706, the bi-directional AC/DC inverter 302 may receive ACelectrical power at its AC end from the AC electrical power bus 306. Insome embodiments, the bi-directional AC/DC inverter 302 may beconfigured to draw a desired amount of AC electrical power from the ACelectrical power bus 306. In some embodiments, the amount of ACelectrical power to draw from the AC electrical power bus 306 may bepredetermined and configured based on the DC electrical power threshold.In some embodiments, the amount of AC electrical power to draw from theAC electrical power bus 306 may be configurable based on the DCelectrical power threshold and the amount of DC electrical power on theDC electrical power bus, such as a comparative value between the DCelectrical power threshold and the amount of DC electrical power on theDC electrical power bus 308. In some embodiments, the control device maydetermine the amount of AC electrical power to draw from the ACelectrical power bus 306 and/or control and/or signal to thebi-directional AC/DC inverter 302 regarding the amount of AC electricalpower to draw from the AC electrical power bus 306.

In block 708, the bi-directional AC/DC inverter 302 may rectify thereceived AC electrical power. The bi-directional AC/DC inverter 302 mayrectify the AC electrical power to DC electrical power. In block 710,the bi-directional AC/DC inverter 302 may provide the DC electricalpower to the DC electrical power bus 308.

In response to determining that the DC electrical power on the DCelectrical power bus 308 does not fall short of the DC electrical powerthreshold (i.e., determination block 702=“No”), the control device mayset the bi-directional AC/DC inverter 302 to export excess DC electricalpower (i.e., the amount of DC electrical power above the DC electricalpower threshold) from the DC electrical power bus 308 in block 712. Insome embodiments, the control device may set the bi-directional AC/DCinverter 302 to export the excess DC electrical power from the DCelectrical power bus 308 in response to the DC electrical power on theDC electrical power bus 308 exceeding of the DC electrical powerthreshold. In other words, in some embodiments, the DC electrical poweron the DC electrical power bus 308 may exceed, not just meet, the DCelectrical power threshold for the control device to set thebi-directional AC/DC inverter 302 to export DC electrical power from theDC electrical power bus 308. The control device may signal and/orcontrol the bi-directional AC/DC inverter 302 to export DC electricalpower.

In block 714, the bi-directional AC/DC inverter 302 may receive at itsDC end the excess DC electrical power from the DC electrical power bus308. In some embodiments, the bi-directional AC/DC inverter 302 may beconfigured to draw an amount of the excess DC electrical power from theDC electrical power bus 308. In some embodiments, the amount of theexcess DC electrical power to draw from the DC electrical power bus 308may be predetermined and configured based on the DC electrical powerthreshold. In some embodiments, the amount of excess DC electrical powerto draw from the DC electrical power bus 308 may be configurable basedon the DC electrical power threshold and the amount of DC electricalpower on the DC electrical power bus 308, such as a comparative valuebetween the DC electrical power threshold and the amount of DCelectrical power on the DC electrical power bus 308. In someembodiments, the control device may determine the amount of the excessDC electrical power to draw from the DC electrical power bus 308 and/orcontrol and/or signal to the bi-directional AC/DC inverter 302 theamount of DC electrical power to draw from the DC electrical power bus308.

In block 716, the bi-directional AC/DC inverter 302 may invert thereceived excess DC electrical power to AC electrical power. In block718, the bi-directional AC/DC inverter 302 may provide the AC electricalpower to the AC electrical power bus 306.

FIG. 8 illustrates a method 800 for managing fuel cell microgrid systemin a grid connected configuration (i.e., when the microgrid iselectrically connected to the electrical power utility grid 316)according to various embodiments. The method 800 may be implementedusing one or more controllers 314 configured to receive signals fromand/or send control signals to any number or combination ofbi-directional AC/DC inverters 302, AC electrical power busses 306, DCelectrical power busses 308, and/or auxiliary electrical power storageunits 500. In order to encompass the alternative configurations providedin various embodiments, the hardware implementing the method 800 isreferred to herein as a “control device.” Blocks 702-718 may beimplemented in a similar manner as described herein with reference tolike reference numbers of the method 700 with reference to FIG. 7 , andwill not be described again.

Following providing the DC electrical power to the DC electrical powerbus 308 in block 710, the control device may determine whether the ACelectrical power on the AC electrical power bus 306 (e.g., powerprovided from the other power module cluster(s) 310 via the otherinverter(s) 302 and/or from the optional storage device 500) issufficient to rectify to DC electrical power and meet the DC electricalpower threshold in optional determination block 802. In someembodiments, the controller 314 may directly measure and/or interpretreceived signals as the voltage and/or current available from the ACelectrical power bus 306, for example, at and/or from the bi-directionalAC/DC inverter 302. The control device may calculate whether rectifyingan amount of AC electrical power available on the AC electrical powerbus 306 provides sufficient DC electrical power to the DC electricalpower bus 308 to meet the DC electrical power threshold. In someembodiments, the controller 314 may directly measure and/or interpretreceived signals as the voltage and/or current available from the DCelectrical power bus 308, for example, at and/or from the bi-directionalAC/DC inverter 302. The control device may determine whether the DCelectrical power provided by the bi-directional AC/DC electricalinverter 302, by rectifying an amount of AC electrical power availableon the AC electrical power bus 306, provides sufficient DC electricalpower to the DC electrical power bus 308 to meet the DC electrical powerthreshold. The control device may compare the calculated and/or providedDC electrical power to the DC electrical power threshold to determinewhether the AC electrical power on the AC electrical power bus 306 issufficient to meet the DC electrical power threshold.

In response to determining that the AC electrical power on the ACelectrical power bus 306 is sufficient to meet the DC electrical powerthreshold (i.e., optional determination block 802=“Yes”), the controldevice may return to determination block 702 to determine whether the DCelectrical power on a DC electrical power bus 308 falls short of the DCelectrical power threshold in determination block 702. In response todetermining that the AC electrical power on the AC electrical power bus306 is not sufficient to meet the DC electrical power threshold (i.e.,optional determination block 802=“No”), the control device may proceedto optional determination block 804.

In the optional determination block 804, the control device maydetermine a source of AC electrical power to meet the DC electricalpower threshold. For example, the control device may determine whethersufficient AC electrical power is available from the electrical powerutility grid 316 and/or from the auxiliary electrical power storage unit500. The control device then returns to block 706.

FIG. 9 illustrates a method 900 for managing the auxiliary electricalpower storage units 500, and/or electrical power dissipation units 502fuel cell microgrid system according to the embodiment illustrated inFIG. 5 . The method 900 may be implemented using one or more controllers314 configured to receive signals from and/or send control signals toany number or combination of bi-directional AC/DC inverters 302, ACelectrical power busses 306, auxiliary electrical power storage units500, and/or electrical power dissipation units 502. In order toencompass the alternative configurations provided in variousembodiments, the hardware implementing the method 900 is referred toherein as a “control device.”

In determination block 902, the control device may determine (e.g.,using methods described above) whether there is excess AC electricalpower on the AC electrical power bus 306. Excess AC electrical power maybe AC electrical power on the AC electrical power bus 306 in excess ofwhat is needed by the bi-directional AC/DC inverter 302 to providesufficient DC electrical power to a DC electrical power bus 308 to meetthe DC electrical power threshold.

In response to determining that there is excess AC electrical power onthe AC electrical power bus 306 (i.e., determination block 902=“Yes”),the control device may determine whether a charge of an auxiliaryelectrical power storage unit 500 is below a charge capacity thresholdin determination block 904. The control device may directly measureand/or interpret received signals as the voltage and/or currentavailable from the auxiliary electrical power storage unit 500, forexample, at and/or from the auxiliary electrical power storage unit 500.The control device may compare the voltage and/or current of theauxiliary electrical power storage unit 500 to the charge capacitythreshold to determine whether the charge of the auxiliary electricalpower storage unit 500 is below the charge capacity threshold.

In response to determining that the charge of the auxiliary electricalpower storage unit 500 is below the charge capacity threshold (i.e.,determination block 904=“Yes”), the control device may charge theauxiliary electrical power storage unit 500 in block 906. The controldevice may signal and/or control the auxiliary electrical power storageunit 500 to import AC electrical power from the AC electrical power bus306. The auxiliary electrical power storage unit 500 may charge usingthe excess AC electrical power on the AC electrical power bus 306 fromthe power module cluster(s) 300 and/or from the grid 316.

In determination block 908, the control device may determine whetherthere is still excess AC electrical power on the AC electrical power bus306 after charging the storage unit 500. The control device maydetermine whether there is excess AC electrical power on the ACelectrical power bus 306 in a manner similar as described herein forblock 902. In addition, the control device may directly measure and/orinterpret received signals as the voltage and/or current available onthe AC electrical power bus 306, for example, at and/or from anelectrical power dissipation unit 502.

In response to determining that the charge of the auxiliary electricalpower storage unit 500 is not below the charge capacity threshold (i.e.,determination block 904=“No” because the storage unit 500 is fullycharged), or in response to determining that there is still excess ACelectrical power on the AC electrical power bus 306 after charging thestorage unit 500 (i.e., determination block 908=“Yes”), the controldevice may dissipate excess AC electrical power on the AC electricalpower bus 306 in block 910 by providing the excess AC electrical powerto the electrical power dissipation unit 502.

In response to determining that there is not excess AC electrical poweron the AC electrical power bus 306 (i.e., determination block 908=“No”),or following dissipating excess AC electrical power on the AC electricalpower bus 306 in block 910, the control device may return todetermination to block 902 to continue to determine whether there isexcess AC electrical power on the AC electrical power bus 306 indetermination block 902.

The methods and systems of the embodiments of the present disclosureimprove power utilization of paralleled power module clusters. Forexample, if there are two power module clusters 300 each containing fivepower modules 12, then the DC electrical power which equals to the DCelectrical power threshold is provided from all ten power modules 12 tothe AC load 312 via the two uninterruptible power modules 304. If theAC/DC inverters 302 are not bi-directional, then when one of the tenpower modules 12 (e.g., power module 1 in cluster M) fails, the maximumpower available to the AC load 312 from the two power module clusters300 is 20% less than the DC electrical power threshold because the twouninterruptible power modules 304 are configured to output the sameamount of power (e.g., 40% each of the AC load demand). In this case,the additional 20% of the power has to be drawn from the utility grid316, which means that the power module cluster 300 (e.g., cluster 1) inwhich all five power modules 12 are operating at the desired poweroutput is underutilized for supplied power to the AC load.

However, by using bi-directional AC/DC inverters 302 of the embodimentsof the present disclosure, the power lost from one power module cluster300 containing the failed power module, can be made up from the otherpower module cluster 300 in which all power modules are operating at thedesired power output. In other words, when one or more power modules 12fail or degrade in one “weak” power module cluster 300, then that lostpower can be diverted from the other “healthy” power module(s) 300 tothe “weak” power module clusters 300 though grid parallel inverters 302without disturbing the paralleled operation of the uninterruptible powermodules 304.

In this scenario, the “healthy” power module cluster 300 (e.g., cluster1) with all of its power modules 12 are operating at the desired poweroutput is making 50% of the microgrid power output which equals to theDC electrical power threshold, while the “weak” power module cluster 300(e.g., cluster M) is making 40% of the microgrid power output whichequals to the DC electrical power threshold. Thus, 5% of the poweroutput of the “healthy” power module cluster 300 is directed to the“weak” power module cluster via the bi-directional AC/DC inverters 302connected together by the AC power bus 306. In this case, bothuninterruptible power modules 304 output 45% of the power demand of theAC load 312.

The two power module clusters 300 may be designed to output more powerthan 50% of the power demand of the AC load 312. In this case, the lostpower can be diverted from the other “healthy” power module 300 to the“weak” power module cluster 300 to satisfy the enter power demand of theAC load 312.

In one embodiment, the amount of power and its direction is controlledby the controller 314 based on the voltages of the DC electrical powerbuses 308. When the voltage on a particular DC electrical power bus 308drops below a threshold value, the controller 314 notes the deficiencyin power on the given DC electrical power bus 308 and changes thedirection of the corresponding bi-directional AC/DC inverter 302 frompower export to power import and optionally provides power from theelectrical power utility grid 316 and/or the storage unit 500 to thecorresponding DC electrical power bus 308 until the voltage on that DCelectrical power bus recovers to a desired threshold value. The DCelectrical power bus 308 voltage recovery limit automatically determinesthe amount of power required (if any) from the electrical utility powergrid 316 and/or from the storage unit 500. Similarly when the DCelectrical power bus 308 voltage increases, then the bi-direction AC/DCinverter 302 changes its power direction to export and start increasingthe export power until the DC electrical power bus 308 voltage reaches adesired value.

In some embodiments, the methods 600, 700, 800, 900 may be implementedin series and/or in parallel. The methods 600, 700, 800, 900 may beperiodically, repetitively, and/or continuously implemented.

According to one embodiment, a microgrid system includes a first directcurrent (DC) power source 300 (e.g., cluster 1) electrically connectedto a first DC electrical power bus 308, a second DC power source 300(e.g., cluster M) electrically connected to a second DC electrical powerbus 308, a first uninterruptable power module 304 (e.g., module 1)electrically connected to the first DC electrical power bus 308 andconfigured to be connected to an alternating current (AC) load 312, asecond uninterruptable power module 304 (e.g., module Q) electricallyconnected to the second DC electrical power bus 308 and configured to beconnected to the AC load 312, a first bi-directional AC/DC inverter 302(e.g., inverter 1) having a DC end and an AC end, wherein the first DCelectrical power bus 308 is connected to the DC end of the firstbi-directional AC/DC inverter 302, a second bi-directional AC/DCinverter 302 (e.g., inverter P) having a DC end and an AC end, whereinthe second DC electrical power bus 308 is connected to the DC end of thesecond bi-directional AC/DC inverter 302, and an AC electrical power bus306 electrically connected to the first and the second bi-directionalAC/DC inverters 302 at their AC ends.

In one embodiment, the microgrid system further comprises a controldevice (e.g., controller) 314 configured with control device executablecode configured to cause the control device to execute operationscomprising determining if first DC electrical power output by the firstDC power source 300 to the first DC electrical power bus 308 is lessthan, equal to or greater than a DC electrical power threshold to beprovided to the first uninterruptable power module 304, and in responseto determining that the first DC electrical power is less than the DCelectrical power threshold, importing supplemental AC electrical powerfrom the AC electrical power bus 306 by the first bi-directional AC/DCinverter 302, and providing a second DC electrical power from the firstbi-directional AC/DC inverter 302 to the first DC electrical power bus308, such that the first DC electrical power and the second DCelectrical power are not less than then below the DC electrical powerthreshold.

In one embodiment, the control device 314 is configured with controldevice executable code configured to cause the control device to executeoperations such that in response to determining that the first DCelectrical power is less than the DC electrical power threshold,providing a portion of a DC electrical power output by the second DCpower source 300 to the second bi-directional inverter 302 though thesecond DC electrical power bus 308, and providing a supplemental ACpower from the second bi-directional AC/DC inverter 302 to the ACelectrical power bus 306.

In one embodiment, the control device 314 is configured with controldevice executable code configured to cause the control device to executeoperations such that in response to determining that the first DCelectrical power is greater than the DC electrical power threshold,providing excess DC electrical power which exceeds DC electrical powerthreshold to the first bi-directional AC/DC inverter 302, converting theexcess DC electrical power to additional AC electrical power in thefirst bi-directional AC/DC inverter 302, and exporting the additional ACelectrical power to the AC power bus 306.

In one embodiment, a selective electrical connector 400 is electricallyconnected to the AC electrical power bus 306 and electricallyconnectable to an electrical power utility grid 306. The control device316 is configured with control device executable code configured tocause the control device to execute operations further comprisingdetermining whether AC electrical power is available from the electricalpower utility grid 316, and selectively electrically disconnecting theAC electrical power bus 306 from the electrical power utility grid 316by opening the selective electrical connector 400 in response todetermining that AC electrical power is not available from theelectrical power utility grid.

In one embodiment, the control device 314 is configured with controldevice executable code configured to cause the control device to executeoperations further comprising in response to determining that the firstDC electrical power is less than the DC electrical power threshold:determining whether the supplemental AC electrical power on the ACelectrical power bus 306 is sufficient to meet the DC electrical powerthreshold, and drawing additional AC electrical power from at least oneof the electrical power utility grid 316 or the auxiliary electricalpower storage unit 500 by the first bi-directional AC/DC inverter 302 inresponse to determining that the supplemental AC electrical power on theAC electrical power bus 306 is not sufficient to meet the DC electricalpower threshold.

In one embodiment, the control device 314 is configured with controldevice executable code configured to cause the control device to executeoperations further comprising determining whether excess AC electricalpower is provided on the AC electrical power bus 306, determiningwhether a charge of the auxiliary electrical power storage unit 500exceeds a charge threshold, and charging the auxiliary electrical powerstorage unit 500 using the excess AC electrical power from the ACelectrical power bus 306 in response to determining that there is excessAC electrical power on the AC electrical power bus and that the chargeof the auxiliary electrical power storage unit 500 does not exceed thecharge threshold.

In one embodiment, the control device 314 is configured with controldevice executable code configured to cause the control device to executeoperations further comprising determining whether there is excess ACelectrical power on the AC electrical power bus 306 after charging theauxiliary electrical power storage unit 500 and whether the electricalpower utility grid 316 is electrically connected to the AC electricalpower bus 306, and dissipating the excess AC electrical power from theAC electrical power bus by an electrical power dissipation unit 502 inresponse to determining that there is excess AC electrical power on theAC electrical power bus and that the electrical power utility grid 315is not electrically connected to the AC electrical power bus 306.

In one embodiment, the first DC power source 300 comprises a first fuelcell power module cluster comprising a plurality of first fuel cellpower modules 12, the second DC power source 300 comprises a second fuelcell power module cluster comprising a plurality of second fuel cellpower modules 12, the first DC electrical power is less than the DCelectrical power threshold when at least one first fuel cell powermodule 12 fails or degrades. The first and the second uninterruptablepower modules 304 comprise unidirectional DC/AC inverters. The controldevice 314 is configured with control device executable code configuredto cause the control device to execute operations such that the firstand the second uninterruptable power modules 304 provide a same amountof AC electrical power to the AC load 312.

FIG. 10 illustrates an example of a fuel cell microgrid system havinginverters 402 and a selective electrical connector which comprises anautomatic transfer switch (ATS) 404. In addition to the descriptions ofthe examples illustrated in FIGS. 3 and 4 , the fuel cell microgridsystem includes the ATS 404 and an additional AC electrical power bus406. In this embodiment, the inverters 402 may be either bi-directionalinverters as described above or unidirectional inverters which areconfigured to invert the DC electrical power from the power modulecluster 300 to the AC electrical power bus 306. The electrical powerutility grid 316 is connected to the normal (N) terminal of the ATS 404,the AC electrical power bus 306 is connected to the load (L) terminal ofthe ATS 404, and a first end of the additional AC electrical power bus406 is connected to the emergency (E) terminal of the ATS 404. Thesecond end of the additional AC electrical power bus 406 is connected tothe load electrical power bus 310.

In this mode of operation, when the electrical power utility grid stopssupplying electrical power (i.e., is “lost”) on the normal (N) terminalof the ATS 404, a standalone voltage source (e.g., load 312 connected tothe load electrical power bus 310) is present on the ATS emergency (E)terminal via the additional AC electrical power bus 406. This causes theATS 404 to change position (i.e., connecting the load (L) terminal tothe emergency (E) terminal), which connects the inverters 402 directlyto the load 312 via the additional AC electrical power bus 406 and theload electrical power bus 310. With this connection, the inverters 402can export as a current source to offset the load 312 from theuninterruptable power modules 304.

As shown, uninterruptable power modules 304 still carry equal power, butthe excess power available in the first inverter 402 is able to reachthe load 312. If bidirectional inverters 302 (instead of unidirectionalinverters 402) are used, the power can still flow through the secondbi-directional inverter (P) 302 as described in FIGS. 4 and 5 .Furthermore, in the embodiment of FIG. 10 , the auxiliary power storageunit 500, and/or an electrical power dissipation unit 502 may beoptionally connected to the AC electrical power bus 306, as shown inFIG. 5 .

The foregoing method descriptions and diagrams are provided merely asillustrative examples and are not intended to require or imply that thesteps of the various embodiments must be performed in the orderpresented. As will be appreciated by one of skill in the art the orderof steps in the foregoing embodiments may be performed in any order.Further, words such as “thereafter,” “then,” “next,” etc. are notintended to limit the order of the steps; these words are simply used toguide the reader through the description of the methods.

One or more diagrams have been used to describe exemplary embodiments.The use of diagrams is not meant to be limiting with respect to theorder of operations performed. The foregoing description of exemplaryembodiments has been presented for purposes of illustration and ofdescription. It is not intended to be exhaustive or limiting withrespect to the precise form disclosed, and modifications and variationsare possible in light of the above teachings or may be acquired frompractice of the disclosed embodiments. It is intended that the scope ofthe invention be defined by the claims appended hereto and theirequivalents.

Control elements, including the control device 301 as well as connectedcontrollers described herein, may be implemented using computing devices(such as computer) that include programmable processors, memory andother components that have been programmed with instructions to performspecific functions or may be implemented in processors designed toperform the specified functions. A processor may be any programmablemicroprocessor, microcomputer or multiple processor chip or chips thatcan be configured by software instructions (applications) to perform avariety of functions, including the functions of the various embodimentsdescribed herein. In some computing devices, multiple processors may beprovided. Typically, software applications may be stored in the internalmemory before they are accessed and loaded into the processor. In somecomputing devices, the processor may include internal memory sufficientto store the application software instructions.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention. The hardware used to implement the various illustrativelogics, logical blocks, modules, and circuits described in connectionwith the aspects disclosed herein may be implemented or performed with acontrol device that may be or include a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general-purpose processor may be amicroprocessor, but, in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. Alternatively, some blocks ormethods may be performed by circuitry that is specific to a givenfunction.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use any of the describedembodiments. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thescope of the disclosure. Thus, the claims are not intended to be limitedto the embodiments shown herein but are to be accorded the widest scopeconsistent with the claim language and the principles and novel featuresdisclosed herein.

What is claimed is:
 1. A microgrid system, comprising: a first directcurrent (DC) power source electrically connected to a first DCelectrical power bus; a second DC power source electrically connected toa second DC electrical power bus; a first uninterruptable power moduleelectrically connected to the first DC electrical power bus andconfigured to be connected to an alternating current (AC) load; a seconduninterruptable power module electrically connected to the second DCelectrical power bus and configured to be connected to the AC load; afirst bi-directional AC/DC inverter having a DC end and an AC end,wherein the first DC electrical power bus is connected to the DC end ofthe first bi-directional AC/DC inverter; a second bi-directional AC/DCinverter having a DC end and an AC end, wherein the second DC electricalpower bus is connected to the DC end of the second bi-directional AC/DCinverter; an AC electrical power bus electrically connected to the firstand the second bi-directional AC/DC inverters at their AC ends; and acontrol device communicatively connected to the first bi-directionalAC/DC inverter and the second bi-directional AC/DC inverter andconfigured with control device executable code configured to cause thecontrol device to execute operations comprising: configuring the secondbi-directional AC/DC inverter to provide supplemental AC power to the ACelectrical power bus; and configuring the first bi-directional AC/DCinverter to import at least part of the supplemental AC electrical powerfrom the AC electrical power bus.
 2. The microgrid system of claim 1,wherein the control device configured with control device executablecode configured to cause the control device to execute operationsfurther comprising: determining if first DC electrical power output bythe first DC power source to the first DC electrical power bus is lessthan, equal to or greater than a DC electrical power threshold to beprovided to the first uninterruptable power module; and in response todetermining that the first DC electrical power is less than the DCelectrical power threshold, importing the supplemental AC electricalpower from the AC electrical power bus by the first bi-directional AC/DCinverter, and providing a second DC electrical power from the firstbi-directional AC/DC inverter to the first DC electrical power bus, suchthat the first DC electrical power and the second DC electrical powerare not less than the DC electrical power threshold.
 3. The microgridsystem of claim 2, wherein the control device is configured with controldevice executable code configured to cause the control device to executeoperations such that: in response to determining that the first DCelectrical power is less than the DC electrical power threshold,providing a portion of a DC electrical power output by the second DCpower source to the second bi-directional inverter though the second DCelectrical power bus; and providing the supplemental AC power from thesecond bi-directional AC/DC inverter to the AC electrical power bus. 4.The microgrid system of claim 3, wherein the control device isconfigured with control device executable code configured to cause thecontrol device to execute operations such that: in response todetermining that the first DC electrical power is greater than the DCelectrical power threshold, providing excess DC electrical power whichexceeds DC electrical power threshold to the first bi-directional AC/DCinverter; converting the excess DC electrical power to additional ACelectrical power in the first bi-directional AC/DC inverter; andexporting the additional AC electrical power to the AC power bus.
 5. Themicrogrid system of claim 3, further comprising a selective electricalconnector electrically connected to the AC electrical power bus andelectrically connectable to an electrical power utility grid, whereinthe control device is configured with control device executable codeconfigured to cause the control device to execute operations furthercomprising: determining whether AC electrical power is available fromthe electrical power utility grid; and selectively electricallydisconnecting the AC electrical power bus from the electrical powerutility grid by opening the selective electrical connector in responseto determining that AC electrical power is not available from theelectrical power utility grid.
 6. The microgrid system of claim 5,further comprising an auxiliary electrical power storage unit, whereinthe control device is configured with control device executable codeconfigured to cause the control device to execute operations furthercomprising: in response to determining that the first DC electricalpower is less than the DC electrical power threshold: determiningwhether the supplemental AC electrical power on the AC electrical powerbus is sufficient to meet the DC electrical power threshold; and drawingadditional AC electrical power from at least one of the electrical powerutility grid or the auxiliary electrical power storage unit by the firstbi-directional AC/DC inverter in response to determining that thesupplemental AC electrical power on the AC electrical power bus is notsufficient to meet the DC electrical power threshold.
 7. The microgridsystem of claim 6, wherein the control device is configured with controldevice executable code configured to cause the control device to executeoperations further comprising: determining whether excess AC electricalpower is provided on the AC electrical power bus; determining whether acharge of the auxiliary electrical power storage unit exceeds a chargethreshold; and charging the auxiliary electrical power storage unitusing the excess AC electrical power from the AC electrical power bus inresponse to determining that there is excess AC electrical power on theAC electrical power bus and that the charge of the auxiliary electricalpower storage unit does not exceed the charge threshold.
 8. Themicrogrid system of claim 7, further comprising an electrical powerdissipation unit electrically connected to the AC electrical power bus,wherein the control device is configured with control device executablecode configured to cause the control device to execute operationsfurther comprising: determining whether there is excess AC electricalpower on the AC electrical power bus after charging the auxiliaryelectrical power storage unit and whether the electrical power utilitygrid is electrically connected to the AC electrical power bus; anddissipating the excess AC electrical power from the AC electrical powerbus by the electrical power dissipation unit in response to determiningthat there is excess AC electrical power on the AC electrical power busand that the electrical power utility grid is not electrically connectedto the AC electrical power bus.
 9. The microgrid system of claim 2,wherein: the first DC power source comprises a first fuel cell powermodule cluster comprising a plurality of first fuel cell power modules;the second DC power source comprises a second fuel cell power modulecluster comprising a plurality of second fuel cell power modules; andthe first DC electrical power is less than the DC electrical powerthreshold when at least one first fuel cell power module fails ordegrades.
 10. The microgrid system of claim 2, wherein: the first andthe second uninterruptable power modules comprise unidirectional DC/ACinverters; and the control device is configured with control deviceexecutable code configured to cause the control device to executeoperations such that the first and the second uninterruptable powermodules provide a same amount of AC electrical power to the AC load. 11.A method of operating the microgrid system of claim 1, comprising:providing a same amount of AC electrical power to the AC load from thefirst and the second uninterruptable power modules; providing thesupplemental AC power from the second bi-directional AC/DC inverter tothe AC electrical power bus; and importing the at least part of thesupplemental AC electrical power from the AC electrical power bus by thefirst bi-directional AC/DC inverter.
 12. The method of operating themicrogrid system of claim 11, further comprising: determining if a firstDC electrical power output by the first DC power source to the first DCelectrical power bus is less than, equal to or greater than a DCelectrical power threshold to be provided to the first uninterruptablepower module; and in response to determining that the first DCelectrical power is less than the DC electrical power threshold,importing the supplemental AC electrical power from the AC electricalpower bus by the first bi-directional AC/DC inverter, and providing asecond DC electrical power from the first bi-directional AC/DC inverterto the first DC electrical power bus, such that the first DC electricalpower and the second DC electrical power are not less than the DCelectrical power threshold.
 13. The method of operating the microgridsystem of claim 12, further comprising: in response to determining thatthe first DC electrical power is less than the DC electrical powerthreshold, providing a portion of a DC electrical power output by thesecond DC power source to the second bi-directional inverter though thesecond DC electrical power bus, and providing the supplemental AC powerfrom the second bi-directional AC/DC inverter to the AC electrical powerbus.
 14. The method of operating the microgrid system of claim 13,further comprising: in response to determining that the first DCelectrical power is greater than the DC electrical power threshold,providing excess DC electrical power which exceeds DC electrical powerthreshold to the first bi-directional AC/DC inverter; converting theexcess DC electrical power to additional AC electrical power in thefirst bi-directional AC/DC inverter; and exporting the additional ACelectrical power to the AC power bus.
 15. The method of operating themicrogrid system of claim 13, further comprising: determining whether ACelectrical power is available from an electrical power utility grid; andselectively electrically disconnecting the AC electrical power bus fromthe electrical power utility grid in response to determining that ACelectrical power is not available from the electrical power utilitygrid.
 16. The method of operating the microgrid system of claim 15,further comprising: in response to determining that the first DCelectrical power is less than the DC electrical power threshold:determining whether the supplemental AC electrical power on the ACelectrical power bus is sufficient to meet the DC electrical powerthreshold; and drawing additional AC electrical power from at least oneof the electrical power utility grid or an auxiliary electrical powerstorage unit by the first bi-directional AC/DC inverter in response todetermining that the supplemental AC electrical power on the ACelectrical power bus is not sufficient to meet the DC electrical powerthreshold.
 17. The method of operating the microgrid system of claim 16,further comprising: determining whether excess AC electrical power isprovided on the AC electrical power bus; determining whether a charge ofthe auxiliary electrical power storage unit exceeds a charge threshold;and charging the auxiliary electrical power storage unit using theexcess AC electrical power from the AC electrical power bus in responseto determining that there is excess AC electrical power on the ACelectrical power bus and that the charge of the auxiliary electricalpower storage unit does not exceed the charge threshold.
 18. The methodof operating the microgrid system of claim 17, further comprising:determining whether there is excess AC electrical power on the ACelectrical power bus after charging the auxiliary electrical powerstorage unit and whether the electrical power utility grid iselectrically connected to the AC electrical power bus; and dissipatingthe excess AC electrical power from the AC electrical power bus inresponse to determining that there is excess AC electrical power on theAC electrical power bus and that the electrical power utility grid isnot electrically connected to the AC electrical power bus.
 19. Themethod of operating the microgrid system of claim 12, wherein: the firstand the second uninterruptable power modules comprise unidirectionalDC/AC inverters; the first DC power source comprises a first fuel cellpower module cluster comprising a plurality of first fuel cell powermodules; the second DC power source comprises a second fuel cell powermodule cluster comprising a plurality of second fuel cell power modules;and the first DC electrical power is less than the DC electrical powerthreshold when at least one first fuel cell power module fails ordegrades.
 20. The method of operating the microgrid system of claim 12,wherein: the step of determining if first DC electrical power output bythe first DC power source to the first DC electrical power bus is lessthan, equal to or greater than a DC electrical power threshold comprisesmeasuring a voltage on the first DC electrical power bus, anddetermining if the measured voltage is less than, equal to or greaterthan a threshold voltage; and if the measured voltage drops below thethreshold voltage, then a current flow direction of the firstbi-directional AC/DC inverter changes from power export to power importto provide additional electrical power from the AC electrical power busto the first DC electrical power bus until the measured voltage on thatDC electrical power bus recovers to equal the threshold voltage.
 21. Amicrogrid system, comprising: a first direct current (DC) power sourceelectrically connected to a first DC electrical power bus; a second DCpower source electrically connected to a second DC electrical power bus;a first uninterruptable power module electrically connected to the firstDC electrical power bus and configured to be connected to an alternatingcurrent (AC) load via at least one load electrical power bus; a seconduninterruptable power module electrically connected to the second DCelectrical power bus and configured to be connected to the AC load viathe at least one load electrical power bus; a first AC/DC inverterhaving a DC end and an AC end, wherein the first DC electrical power busis connected to the DC end of the first AC/DC inverter; a second AC/DCinverter having a DC end and an AC end, wherein the second DC electricalpower bus is connected to the DC end of the second AC/DC inverter; anautomatic transfer switch (ATS) having a load terminal, an emergencyterminal, and a normal terminal configured to be connected to anelectrical power utility grid; a first AC electrical power buselectrically connected to the first and the second AC/DC inverters attheir AC ends, and electrically connected to the load terminal of theATS; and a second AC electrical power bus electrically connected to theemergency terminal of the ATS and to the at least one load electricalpower bus.
 22. A microgrid system, comprising: a first direct current(DC) power source electrically connected to a first DC electrical powerbus; a second DC power source electrically connected to a second DCelectrical power bus; a first uninterruptable power module electricallyconnected to the first DC electrical power bus and configured to beconnected to an alternating current (AC) load; a second uninterruptablepower module electrically connected to the second DC electrical powerbus and configured to be connected to the AC load; a firstbi-directional AC/DC inverter having a DC end and an AC end, wherein thefirst DC electrical power bus is connected to the DC end of the firstbi-directional AC/DC inverter; a second bi-directional AC/DC inverterhaving a DC end and an AC end, wherein the second DC electrical powerbus is connected to the DC end of the second bi-directional AC/DCinverter; an AC electrical power bus electrically connected to the firstand the second bi-directional AC/DC inverters at their AC ends; acontrol device configured with control device executable code configuredto cause the control device to execute operations comprising:determining if first DC electrical power output by the first DC powersource to the first DC electrical power bus is less than, equal to orgreater than a DC electrical power threshold to be provided to the firstuninterruptable power module; and in response to determining that thefirst DC electrical power is less than the DC electrical powerthreshold: providing a portion of a DC electrical power output by thesecond DC power source to the second bi-directional inverter though thesecond DC electrical power bus; providing supplemental AC power from thesecond bi-directional AC/DC inverter to the AC electrical power bus;importing supplemental AC electrical power from the AC electrical powerbus by the first bi-directional AC/DC inverter; and providing a secondDC electrical power from the first bi-directional AC/DC inverter to thefirst DC electrical power bus, such that the first DC electrical powerand the second DC electrical power are not less than the DC electricalpower threshold.
 23. A method of operating a microgrid systemcomprising: a first direct current (DC) power source electricallyconnected to a first DC electrical power bus; a second DC power sourceelectrically connected to a second DC electrical power bus; a firstuninterruptable power module electrically connected to the first DCelectrical power bus and configured to be connected to an alternatingcurrent (AC) load; a second uninterruptable power module electricallyconnected to the second DC electrical power bus and configured to beconnected to the AC load; a first bi-directional AC/DC inverter having aDC end and an AC end, wherein the first DC electrical power bus isconnected to the DC end of the first bi-directional AC/DC inverter; asecond bi-directional AC/DC inverter having a DC end and an AC end,wherein the second DC electrical power bus is connected to the DC end ofthe second bi-directional AC/DC inverter; and an AC electrical power buselectrically connected to the first and the second bi-directional AC/DCinverters at their AC ends, the method comprising: providing a sameamount of AC electrical power to the AC load from the first and thesecond uninterruptable power modules; determining if a first DCelectrical power output by the first DC power source to the first DCelectrical power bus is less than, equal to or greater than a DCelectrical power threshold to be provided to the first uninterruptablepower module; and in response to determining that the first DCelectrical power is less than the DC electrical power threshold,importing supplemental AC electrical power from the AC electrical powerbus by the first bi-directional AC/DC inverter, and providing a secondDC electrical power from the first bi-directional AC/DC inverter to thefirst DC electrical power bus, such that the first DC electrical powerand the second DC electrical power are not less than the DC electricalpower threshold.